1. Field of the Invention
The present invention relates generally to a visible light communication system which makes use of visible light, and more particularly to a visible light communication system which makes use of a multiplexed visible light signal in which RGB visible lights are multiplexed.
2. Description of the Related Art
In recent years, a visible light communication system which makes use of visible light has steadily been developed. There have been proposed visible light communication systems which use, as light sources, light-emitting diodes (LEDs) or light sources for illumination (see, e.g. Patent Document 1).
Also proposed is a visible light communication technique wherein information is transmitted by light communication by flickering LEDs at such a high speed that visual recognition is impossible (see, e.g. Patent Document 2).
Visible light communication systems adopt, as communication methods, such modulation methods as AM (amplitude modulation), FM (frequency modulation) and PM (pulse modulation), which are based on variations in luminance of visible light. Specifically, visible light, which is emitted from a light source, is modulated in accordance with transmission data (digital signal string), and the modulated light is transmitted as a visible light signal.
In the meantime, in the communication method using an LED as a light source, white light is, in general, emitted by combining lights of the three primary colors (also expressed as RGB) of red (R), green (G) and blue (B), and the white light is modulated. In addition, there is known a communication method in which the emission amount of light of an LED is varied in accordance with a signal waveform of information to be transmitted, and the light with the varied emission amount is transmitted (see, e.g. Patent Document 3).
Patent Document 1: Jpn. Pat. Appln. KOKAI Publication No. 2004-221747,
Patent Document 2: Jpn. Pat. Appln. KOKAI Publication No. 2002-202741, and
Patent Document 3: Jpn. Pat. Appln. KOKAI Publication No. 2004-147063.
In a visible light communication system using the LED as a light source, the sizes of a transmission device and a reception device can be reduced and the power consumption can be decreased. Thus, this communication system is useful as a communication system which employs a mobile phone, for instance. However, in a case where high-speed communication is to be realized by increasing the modulation speed, it is difficult to realize such high-speed communication because of, e.g. responsivity characteristics of the LED.
The object of the present invention is to provide a visible light communication system wherein high-speed communication is enabled, in particular, without increasing a modulation speed, by realizing multiplex visible light communication in which visible lights of RGB are multiplexed.